The present invention relates to methods and apparatus for exercising and/or testing the lumbar muscles of the human body. Such methods and apparatus are disclosed for example in my U.S. Pat. Nos. 4,836,536 and 4,902,009. With these methods and apparatus, the subject is seated in a generally upright position with his pelvis fixed against movement and the subject's lumbar muscles are exercised by having the subject impose with the lumbar muscles forces against a movement arm to pivot the latter about a horizontal axis against the bias of a resistance preferably one or more dead weights. To increase the efficiency of the exercise as well as the accuracy of measurement of the subject's strength, the weight of the subject's torso is counterweighted since the mass of the torso during testing or exercise of the lumbar extension muscles may produce as little as a few foot-pounds of torque or as much as a hundred foot-pounds of torque or more. However although counterweighting has significantly increased accuracy and efficiency, since in actual practice, the subject's torso pivots about an axis which changes depending on the position of the torso and further since the counterweighting of the torso is calibrated for only one position of the torso prior to the exercise (albeit the position where the weight of the torso would have the most adverse effect on the accuracy of the measurement), the adverse effect of the subject's torso weight on accuracy and efficiency has not been entirely eliminated by counterweighting.
The present invention provides another method and apparatus for exercising the lumbar muscles of the human body while at the same time substantially eliminating the adverse effect of the subject's torso on the efficiency of the exercise and accuracy of the testing of the lumbar muscles.